<!DOCTYPE html>
<html>
<head>
	<meta charset="utf-8">
	<meta name="viewport" content="width=device-width, initial-scale=1">
	<title></title>
</head>
<body>

</body>
</html>

<script>
	var str = "hello";
	var a = 10;
	var b = 2;
	var c = 3;
	var d = "20";
	var e = "20a"
	//alert(a-d);
	//alert(a/d);
	alert(a-e)

	document.write(a+b+str+"\n");
	document.write("<br/>");
	document.write(str+true);
	document.write("<br/>")
	document.write(str+null);
	document.write("<br/>")
	document.write(str+NaN);
	document.write("<br/>")
	document.write(str+undefined);
	document.write("<br/>")
	document.write(a-b+"\n");
	document.write(a*b+"\n");
	document.write(a/b+"\n");
	document.write(a%c+"\n");
</script>